But Andreas Rupprecht, a German researcher focused on China's air power, recently posted an informational brochure from the Aviation Industry Corporation of China, the J-20's maker, laying out its mission.

AVIC calls the J-20 a "heavy stealth" fighter that's "renowned" for its dominance in medium and long-range air combat and lists first "seizing & maintaining air superiority" as its core missions.

J-20 loses the old fashioned fight for the skies

Two J-20 stealth fighter jets of the Chinese People's Liberation Army (PLA) Air Force performs during the 12th China International Aviation and Aerospace Exhibition, also known as Airshow China 2018, Tuesday, Nov. 6, 2018, in Zhuhai city, south China's Guangdong province.AP Photo/Kin Cheung

Justin Bronk, an aerial combat expert at the Royal United Services Institute, told Business Insider for the J-20, fighting US or European jets for control of the skies represents a losing battle.

The J-20 is "certainly likely to be more capable as an air superiority platform than anything else the People's Liberation Army Air Force (China's air force's official name) is currently operating," said Bronk.

"With a powerful radar and multiple internal air-to-air missiles as well as long range, it certainly shouldn't be dismissed as an air superiority machine," he continued.

But just because it's China's best doesn't mean it can hold a candle to Europe's Typhoon fighter or even the US's F-15, which first flew in 1972.

"In terms of thrust to weight, maneuverability and high altitude performance it is unlikely to match up to the US or European air superiority fighters," said Bronk.

China's J-20 made a solid entry into the world of stealth fighter aircraft and became the only non-US stealth jet in the world. Its design should significantly limit the ability of US radar to spot and track the large fighter, but the stealth mainly works on the front end, while the J-20 is flying straight towards the radar.

Tactically, experts have told Business Insider the J-20 poses a serious threat in the interception and maritime strike roles with its stealth design, but so far the jet has yet to deliver.

China has suffered embarrassing setbacks in domestically building jet engines that would give the J-20 true fifth-generation performance on par with the F-35 or F-22.

Bronk said China still appears years away from crossing this important threshold that will increase the range and performance of the jets.

"The engines are a significant limiting factor" in that they require inefficient use of afterburners and limit high-altitude performance, said Bronk.

What air superiority looks like

An F-15C Eagle prepares to refuel with a KC-135R Stratotanker Sept. 12, 2013, en route to the Arctic Challenge Exercise in Norway.US Air Force Photo

As it stands, the J-20 couldn't match the F-15, the Eurofighter Typhoon, or even get close to an F-22, said Bronk.

"Against the F-15C and Typhoon the J-20 has a lower radar cross section but worse performance and its air to air missiles are unlikely to yet match the latest [US] series, and certainly not the new European Meteor," said Bronk.

Bronk pointed out that China has made great strides in air-to-air missile development and is testing at an "extremely high" pace, so the capability gap could close in a few short years.

But how does the J-20 stack up to the greatest air superiority plane on the planet today, the F-22?

"The F-22 likely significantly out-performs the J-20 in almost every aspect of combat capability except for combat radius," said Bronk, refering to the farthest distance a loaded plane can travel without refueling.

Undoubtedly the J-20 represents a significant leap in Chinese might and poses a serious and potentially critical threat US air power in its ability to intercept and launch deep strikes.

But in the narrow role of air superiority, which means beating the best fighters the other side can offer to gain control of the sky, the US and Europe can likely beat down China's J-20 without much trouble.